JP4867044B2 - Column replacement construction method - Google Patents

Description

  The present invention relates to a column replacement construction method as a foundation method for civil engineering and building structures.

  As a basic construction method for civil engineering and building structures, a deep mixing method, a fluidized earth method, a PIP pile method, an RG pile method, and the like have been proposed.

  The deep mixing treatment method is a method of constructing a cylindrical ground improvement body in the ground by inserting an excavation stirring mixing device into the ground and mixing with the original ground at the same time while filling the solidified material (for example, patent There are a method of filling the solidified material when the excavating and stirring mixing device is dug into the ground, and a method of filling the solidified material when it is pulled upward. Moreover, there are a method of using the solidified material in a slurry form by stirring and mixing with water, and a method of using the solidified material in powder form.

  The fluidized earth method is to improve the ground by mixing the earth and sand excavated with a continuous spiral auger with solidified material with a ground mixer to make soil cement, and then returning the soil cement to the place where it was excavated again. (For example, see Patent Documents 2 and 3).

  In the PIP pile method, a driving device is attached to the head of a hollow shaft of an auger with continuous flights, the entire device is suspended on a fence, excavated to a predetermined depth while rotating in the ground, a predetermined depth Is reached, a mortar pile is formed by gradually pulling up the mortar from the shaft tip, and immediately after the auger is pulled up, a reinforcing bar or a shaped steel is built into the mortar pile (for example, Patent Document 4 and Non-patent document 1).

In the RG pile method, the earth auger with a hollow shaft rotates to excavate the earth and sand up to a predetermined depth, and then the auger is pulled up and mortar is injected from the outlet of the hollow shaft auger head. A cast-in-place pile is created in the ground (for example, see Non-Patent Document 1).
JP 2003-247228 A (Claim 3, paragraph number 0002) JP-A-8-260450 (Claim 1) Japanese Patent No. 3280710 (Claim 1) Japanese Patent No. 3306460 (paragraph number 0002) Underground Continuous Wall Construction Method Design and Construction Handbook edited by Japan Construction Mechanization Association, published by Gihodo Publishing Co., Ltd. (pp. 427 to 430)

The above-mentioned deep mixing treatment method has the following problems.
(1) Because it is a construction method to build a ground improvement body in the ground by mixing with the original ground while filling the solidified material at the same time, it is improved due to the fact that the soil physical properties of the ground to be improved are not constant The soil quality has the disadvantage that the uniaxial compressive strength varies greatly. Therefore, the target strength to be improved has to be made larger than the design strength by an amount corresponding to the variation, and the amount of solidifying material added increases, which is uneconomical.

(2) In the deep mixing treatment method, in the viscous ground with high adhesive strength, mixing failure occurs due to the occurrence of the co-rotation phenomenon, and the target quality is often not secured.
(3) In soil layers that contain a large amount of organic matter such as organic soil and peat, and volcanic ash-like clay soils such as loam and red and black black, the solidified material may be hardened, resulting in target quality. It was often impossible to secure.
(4) The ground containing a large amount of organic matter is uneconomical because it requires a large amount of solidifying material.
(5) If the ground is composed of multiple soil layers, it will fill the entire depth range with the amount of solidification material required for the soil layer with the lowest strength development. The amount of solidifying material had to be added, which was uneconomical. In addition, the amount of construction generated soil (residual soil) increased, and the load on the environment was large.

(6) Even if agitation and mixing are performed reliably, the strength of soil cement depends on the soil to be improved. Therefore, if an unexpected soil appears, the improved strength will not reach the target value. There was a risk of poor construction.
(7) In the deep mixing treatment method, it is necessary to improve a larger area to support the same load due to the low expression strength even if a large amount of solidified material such as humus or organic soil is added. there were. Along with this, not only the amount of soil to be improved required for ground improvement increases, but also the footing volume of the foundation increases, so the construction cost has increased.

The fluidized earth method also has the following problems.
(1) Since the local earth and sand are mixed with the ground mixer, the locally generated earth and sand are used. Therefore, the quality after the improvement varies greatly due to the soil physical properties and soil quality variations. There is a drawback. Further, since the local earth and sand and the solidified material are mixed, a large amount of cement is required to obtain the required -axial compressive strength, which may be uneconomical.

(2) Since the excavated soil is discharged to the ground, mixed with the solidified material by a ground mixer to form a slurry-like fluidized soil, and returned to its original position, the number of construction steps increases and costs are reduced. high.
(3) Although it is temporary, since the earth and sand at the location to be improved are excavated and removed, the stress balance due to the overload until then is lost and the supporting ground is loosened. For this reason, the supporting force of the excavation bottom ground is reduced.
(4) If the bottom surface from which the earth and sand have been removed is not carefully treated, the initial settlement problem similar to the tip slime of cast-in-place piles occurs when a vertical load from the structure is applied.

Furthermore, the PIP pile method and the RG pile method have the following problems.
(1) It is necessary to control the moisture content of the fine aggregate used for mortar production, resulting in variations in quality.
(2) Since the mortar contains fine aggregates, the mortar has to use a highly fluid material having a flow value of 18 to 20 seconds, and not only does it easily cause breathing, but also the flow of the mortar. Due to its high nature, excavated earth and sand fall into the mortar, and the earth and sand are mixed into the mortar.

(3) In sandy and gravel soil layers, hole wall collapse due to spring water and groundwater pressure is likely to occur. Therefore, it is necessary to use bentonite mud or a mixture of this with a small amount of cement. is there. In addition, since bentonite becomes sludge, enormous costs are incurred for subsequent processing.
(4) As a result, a slime layer is formed between the bottom surface of the mortar column and the supporting ground, so that a slime treatment step is required.

  In order to solve such problems and to provide a method for constructing a stable quality column without depending on the properties of the target ground, the present applicant digs up while rotating a screw auger having a drilling portion at the tip in the forward direction. After reaching the replacement bottom position of the column, a filler having a table flow value of 150 to 400 mm, which does not contain earth and sand or aggregate, and has a consistency of the filler during kneading or construction, is replaced with the replacement bottom of the column. While discharging from the tip of the screw auger from the position, pull up the auger by forward rotation, and when it reaches the planned replacement upper end position of the column, stop discharging the filler, and then pull up while rotating the auger in the reverse direction Thus, Japanese Patent Application No. 2005-109463 has previously filed a column replacement construction method characterized in that the ground soil is replaced with a filler.

  However, when a high support force is desired for the replaced column, depending on the building conditions, there may be a risk that the initial settlement of the column will be large. May become excessive. That is, when the vertical load of the structure is applied to the replacement column, there is a risk that the initial subsidence increases and the subsidence amount exceeds the allowable value.

  The present invention has been proposed to solve such problems, and its purpose is to prevent the initial subsidence of a replacement column that is replaced with a filler whose consistency is 150 to 400 mm as a table flow value. It is to provide a replacement construction method.

  The column replacement construction method according to the present invention is a position where the screw auger having a drilling portion at the front end is rotated forward and at least about 10 cm above the planned replacement bottom position of the column, at most about the diameter of the replacement column to be built at most. After reaching the upper limit, the filler does not contain earth or sand and the consistency of the filler at the time of kneading or construction is 150 to 400 mm in terms of the table flow value, while discharging forward from the tip of the screw auger. After reaching the replacement bottom position of the column, the ground soil is replaced with the filler by pulling up the screw auger while rotating it forward or backward while discharging the filler from the tip of the screw auger. It is characterized by having a column.

In this invention, the forward rotation of the screw auger refers to a rotation in which excavated soil in the ground is discharged to the ground side by the screw auger.
In addition, the expression “forward rotation” or “reverse rotation” includes an expression that includes substantially no rotation, and the expression “substantially no rotation” can be regarded as not being rotated or substantially not rotating. It is also an expression including the state of forward rotation or reverse rotation at a very low speed.

  For example, when the tip of the replaced column is built on a good support ground with an N value of 30 or more (20 or more depending on the load conditions, etc.), the column is scheduled for rotating excavation claw (blade) during excavation As shown in FIG. 5B, a crack 4 occurs in the original ground G below the replacement bottom, and the original ground G below the planned replacement bottom L1 of the column is disturbed and loosened. As a result, the structure The present inventors have found that the initial subsidence amount of the replacement column may increase when a load from is applied.

  Therefore, after reaching the position at least about 10 cm above the planned replacement bottom position of the column and at most about the diameter of the replacement column to be built, the consistency of the filler not including earth and sand and aggregate and when kneading or construction. When a filler having a table flow value of 150 to 400 mm is excavated in a forward rotation while being discharged from the tip of the screw auger, the filler is filled in the crack 4 as shown in FIG. It was discovered that the initial settlement of the column was reduced.

  If the filler discharge start position above the planned replacement bottom position of the column is lowered, there is a risk that the effect of preventing the initial settlement will be reduced, and the filling from the top of the screw auger from the high position above the planned replacement bottom position of the column may occur. When excavating while discharging material, the amount of filler discharged increases, the filler is mixed with the earth and sand discharged when the screw auger is pulled up, the amount increases, and the amount of filler discharged is mixed accordingly. The amount of soil that has not been reduced. Therefore, the discharged earth and sand becomes an industrial waste mixed with a filler, and the disposal cost is expensive, which is not preferable. Therefore, after reaching the position at least about 10 cm above the planned replacement bottom position of the column and at most about the diameter of the replacement column to be built, it is dug while discharging the filler from the tip of the screw auger. It is possible to reduce the amount of the filler mixed with the earth and sand discharged at the time of pulling up, and to make a replacement column having a small initial settlement when a vertical load from the structure is applied.

  The excavation part refers to any of the following parts. If you have a drilling claw that protrudes from the tip of the screw auger shaft in addition to the drilling blade that has a drilling claw attached to the tip of the spiral auger located at the tip of the screw auger, If the excavating blade and the excavating claw protruding from the screw auger shaft tip are excavation parts, and there is no excavating claw protruding from the screw auger shaft tip, the spiral blade located at the screw auger tip A drilling wing having a drilling claw at the tip is a drilling part.

  According to this replacement column replacement construction method, since the raw ground and the filler are not stirred and mixed, it is possible to obtain a hardened body (column) having the same quality as that of the state of kneading with the above ground mixer. Compared to columns using the deep mixing method, quality variation can be made extremely small, and the strength of the hardened body (column) can be set arbitrarily by adjusting the filler composition. In addition, it is possible to replace the soil within the predetermined replacement range and leave the soil in the non-replacement region above it without leaving the soil.

Further, when supplying the filler to the screw auger, a snake pump (screw pump) can be used in addition to the squeeze pump and the plunger pump.
When the filler is supplied to the auger by a snake pump (screw type pump) and the filler is discharged from the tip of the auger, the consistency of the filler during kneading or construction is low. However, it is particularly preferable because it can be efficiently constructed.

  The filler may be cement alone or may contain other admixtures or admixtures, and the filler is not particularly limited, but should be a filler that does not contain earth or sand. is there. In the present invention, the aggregate means fine aggregate or coarse aggregate called concrete, and powders such as blast furnace slag and fly ash are not aggregates. When a filler containing earth and sand or aggregate is used, the disadvantages described above occur.

Further, the filler needs to be a filler having a table flow value of 150 to 400 mm in the consistency of the filler during kneading or construction.
In addition, by setting the consistency of the filler at the time of kneading or construction to a table flow value of 150 to 400 mm, preferably 150 to 330 mm, it is possible to ensure fluid fillability in the drilling hole and to collapse the hole wall Furthermore, it is possible to prevent the earth and sand above the replacement range from being replaced and falling into the filler.
If the consistency of the filler at the time of kneading or construction is set to 150 mm to 400 mm in the table flow value, if it is less than 150 mm, the resistance (friction force) in the pipe will increase, and it will take too much time during construction, This is because the construction becomes impossible (discharge is impossible), and when it exceeds 400 mm, there is a high possibility that a large amount of earth and sand is mixed in the solidified body.

Further, as described above, when a filler is supplied to the auger by a snake type pump (screw type pump) and the filler is discharged from the tip of the auger, the filler at the time of kneading or construction Even if the consistency is 150 to 260 mm as a table flow value, the construction can be particularly preferable.
The table flow value is a table flow measured by fixing a plate having a diameter of 500 mm on a flow table having a diameter of 300 mm, instead of the diameter of 300 mm of the flow table defined in the physical test method for cement according to JIS R 5201. Value.

Such a filler can reduce the cost of the filler by using inexpensive fly ash and blast furnace slag powder, and can develop an arbitrary strength by adjusting the blending of the filler. It becomes possible to.
The mixing ratio of fly ash or blast furnace slag powder is 3 to 20 parts by weight of fly ash or blast furnace slag powder with respect to 1 part by weight of cement. It can be used as a filler. Generally, in this case, the water content is 30 to 50% based on the total weight of cement and fly ash or blast furnace slag powder. Blast furnace slag powder is preferably used to increase the compressive strength of the replaced column.

  Further, as a screw auger usable in the column replacement construction method of the present invention, an auger in which the spiral blade is a continuous spiral screw, an auger in which the spiral blade is an intermittent spiral screw, and an auger having a length corresponding to at least the column construction length. An auger covered with a cylindrical casing, an auger in which an edge plate is fixed to an edge of a spiral blade of a continuous spiral auger, and the spiral blade are composed of a plurality of intermittent spiral screws, and at least a column of the intermittent spiral screws. The part directly related to the construction can include an auger having a cylindrical ring fixed on the outer periphery. Of course, an auger in which two spiral blades are provided at the same height and with a phase shifted by 180 degrees may be used.

According to the auger in which the spiral blade is a continuous spiral screw, the replacement work can be easily performed by using a general-purpose spiral screw auger.
According to the auger where the spiral wing is an intermittent spiral screw, in a collapsible ground such as sandy ground or gravelly ground, if excavating with a continuous spiral screw, there is a possibility that the excavated soil may be discharged more than necessary. By using an intermittent spiral screw auger, the amount of soil removal can be reduced and the looseness of the surrounding ground can be reduced. As a result, the disturbance of the supporting ground can be reduced. Further, the outer diameter of the intermittent spiral screw may be the same as the diameter of the excavating blade, but if the outer diameter of the intermittent spiral screw is smaller than the diameter of the excavating blade, the amount of soil removal can be further reduced.

  Further, according to the auger covered with a cylindrical casing having a length corresponding to at least the length of the column construction, the sandy soil layer is used to prevent the earth and sand around the drilling hole from being excessively drawn by the spiral screw. In a gravelly soil layer or the like, even if the ground is prone to collapse due to spring water or groundwater pressure, the replacement with the original ground is more reliable without loosening the surrounding ground. At the same time, the support ground is not loosened, and the initial subsidence of the replaced column is not increased when a vertical load is applied from the structure. The cylindrical casing is mounted coaxially with the screw auger so as to be able to rotate forward and backward relatively, or the casing is inserted so as to be independently rotatable, or fixed so that the casing does not rotate. May be.

Furthermore, according to the auger in which the spiral wing is composed of a plurality of intermittent spiral screws and a cylindrical ring is fixed to the outer periphery of at least a portion of the intermittent spiral screws directly related to column construction, the hole wall collapses. There is an action to prevent, and the replacement with the original ground can be performed as in the case of using the casing with a simple device. Also, the auger removal work of the auger pulled up to the ground can be performed more easily than when the casing is used.
In the case of a screw auger with an edge plate attached to the spiral screw, the possibility that the excavated soil that is being discharged along the screw portion spills out from the screw end portion is further reduced.

  Moreover, the excavation claw provided at the tip of the screw auger shaft and the excavation claw provided at the tip of the spiral blade can be exemplified. The excavating claw of the excavating blade and the excavating claw at the tip of the screw auger shaft exert their power in excavation (especially hard ground). Also good.

  Excavation efficiency is improved by the presence of the excavation part. Further, when the filler replacement upper end portion is shaped with the excavating blade with the excavation claw protruding after the replacement column construction is completed, the upper end portion is shaped according to the shape of the claw, so that irregularities are formed when the filler is consolidated. Therefore, it is necessary to reshape the upper end surface of the replacement column in a subsequent process. By using the flat claws, the column upper end surface can be finished in a flat shape in the replacement step, so that reshaping work becomes unnecessary.

  In addition, as shown in claim 2, while discharging the filler from the tip end portion of the screw auger, the auger is pulled up by normal rotation or reverse rotation, and when the upper end position where the column is to be replaced is reached, the filler is discharged. The column replacement construction method according to claim 1, wherein the auger is pulled up while being stopped and then rotated forwardly or reversely, even when the replacement column has earth and sand above the column, If the table flow value of the filler is 150 to 400 mm, the earth and sand left above the replacement range will not fall into the filler. Therefore, it is a good quality replacement column that does not contain soil. In addition, if the table flow value of the filler is 150 to 330 mm, even if the ground conditions are more likely to collapse, even if there is soil to be left above the column, a good quality replacement column that does not mix dirt, etc. It can be.

The column replacement construction method of the present invention and the replacement column obtained by the method have the following effects.
(1) Regardless of the soil quality and ground variation, replacement at the tip of the column can be performed reliably, making it possible to build a column with almost the same quality as when kneading with a ground mixer, and with uniaxial compression strength. It is possible to build replacement columns with small variations.
(2) According to the column replacement construction method of the present invention, and compared with mortar having high fluidity used in the conventional construction method, the filler used in the present invention can have extremely low fluidity. Therefore, it is possible to prevent the earth and sand above the replacement range from being replaced and falling into the filler. As a result, it is possible to build a column with almost the same quality as when kneaded with an above-ground mixer, and it is possible to build a replacement column with a small variation in uniaxial compression strength.
(3) Also in this invention, the filler used in this invention can be extremely low in fluidity compared to the high fluidity mortar used in the conventional construction method. The earth and sand can be prevented from falling into the replaced filler. As a result, it is possible to replace the inside of the predetermined replacement range and leave the sediment in the non-replacement range above it as it is without discharging.
(4) For the same reason as in (2), quality variation can be greatly reduced as compared with the column by the deep mixing processing method.
(5) For the same reason, it is possible to easily set the strength of the solidified body (column) and realize it.
(6) By adjusting the composition of the filler, it becomes possible to develop an arbitrary strength.
(7) When inexpensive fly ash or blast furnace slag powder is used as a filler in the filler, the cost of the filler can be reduced.

(8) Excavation efficiency is improved by the presence of the excavation part. In addition, when the filler replacement upper end is shaped with the tip of the screw auger shaft provided with the drilling claw or the drilling blade provided with the drilling claw, the upper end is shaped according to the shape of the claw, so when the filler is consolidated Concavities and convexities are formed on the surface. Therefore, it is necessary to reshape the upper end surface of the replacement column in a subsequent process. By using a flat nail, it can be finished in a flat shape in the replacement step, so that reshaping work is unnecessary.
(9) Since the replacement column obtained by the present invention can have a high strength, a column having a small area is sufficient to support the same load as that of the conventional ground improvement column. Therefore, the footing volume of the structure foundation is also reduced, and it is possible not only to reduce the amount of concrete in the footing, but also to reduce the amount of construction generated soil associated with the footing construction, and the construction cost can be greatly reduced.
(10) The replacement column obtained by the present invention has excellent performance as described above, and can be a column with a small initial subsidence when a vertical load from a structure acts on the replacement column.

  Hereinafter, the embodiment of the present invention will be described in detail with reference to the drawings by using an example in which a continuous screw auger having continuous spiral blades is used as the screw auger. The outer diameter of the used screw auger is 600 mm.

First, as shown in FIG. 1 (a), the screw auger 1 is set at the center position of the replacement column to be built, and then the screw auger 1 is dug while rotating forward as shown in FIG. 1 (b).
As shown in FIG. 1 (c), after the screw auger 1 reaches a position 30 cm above the planned replacement bottom position L1 of the column, it does not include earth and sand or aggregate from the tip, and is kneaded or constructed. The excavation is continued while rotating forward while discharging the filler having a consistency of 150 to 400 mm as a table flow value.
As shown in FIG. 1 (d), when the screw auger 1 reaches the planned replacement bottom position L1 of the column, the screw auger 1 does not contain earth and sand or aggregate from the tip of the screw auger 1, and is a consistency of the filler during kneading or construction. The screw auger 1 is pulled up by forward rotation as shown in FIG. 1 (e) while discharging a filler having a tensi of 150 to 400 mm as a table flow value.
When the screw auger 1 is pulled up, it is possible to pull it up in reverse rotation or substantially non-rotation in addition to forward rotation, but in order to prevent the excavated soil from falling into the replacement column, it is possible to rotate forward or substantially. It is more preferable to pull up without rotation.
When the column replacement planned upper end position L2 is reached as shown in FIG. 1 (f), the discharge of the filler is stopped, and then the screw auger 1 is pulled up while being reversely rotated as shown in FIG. 1 (g). Thus, the column 2 in which the ground soil is replaced with the filler is used.
In addition, in the example of FIG. 1, the hollow portion 3 in which no filler exists is present on the ground side.
In addition, it is possible to stop the discharge of the filler and then rotate the screw auger 1 in the forward direction instead of the reverse rotation when pulling up the screw auger 1. It is preferable because excavated soil can be left behind.

The loam ground continued to GL-5.15 m shown in FIG. 2 by the above process, and the test was performed on the ground where a gravel layer having an N value of 50 or more appears below.
The filler used should only have a strength equal to or greater than the ground strength of the ground. Usually, fly ash is used as the main raw material and cement is used, but steel pipes and reinforcing steel rods are used in the replacement column. When a core material such as the above is inserted to obtain a composite structure or a high strength, a material obtained by mixing cement with blast furnace slag as a main raw material is used.
This time, the column loading test of the replacement column is performed, so the column strength is more than the ultimate bearing capacity of the ground. Therefore, the filling material which uses the blast furnace slag that exhibits high strength as the main raw material was used.
This is to prevent the replacement column from being destroyed before the supporting ground is destroyed when the vertical loading test is performed. Specific implementation formulations are shown in Table 1. The blast furnace slag powder used was blast furnace slag fine powder 4000 defined in JIS A6206 “Retail Slag Fine Powder for Concrete”.

  Table 2 shows the table flow value (expressed as TF value in the table) and uniaxial compressive strength of this formulation.

The construction equipment is a 80-ton class three-point support pile driver as a base machine, the mixer is a biaxial forced kneading mixer for concrete, the pump is a screw pump, and the spiral auger has an outer diameter of 600 mm as described above. It was used.
In this embodiment, the ground shown in FIG. 2 was constructed in the process shown in FIG. 1, and the construction process is shown below together with the excavation speed and the discharge amount. The tip position of the replacement column to be constructed, that is, the planned replacement bottom position of the column (hereinafter referred to as a predetermined depth) is GL-5.2 m.

  While rotating the spiral auger forward, it excavates at a speed of 2.0 m per minute from a predetermined depth to a position shallower by 0.3 m, which is the distance equal to the radius of the replacement column. While the spiral auger is rotated forward to a predetermined depth while discharging 100 liters per minute, the digging is carried out at a speed of 2.0 m per minute, and immediately after reaching the predetermined depth, the discharge amount of 100 liters per minute of the filler is maintained, The spiral auger was pulled up at a speed of 0.35 m per minute while rotating forward, and when it reached the position of GL-1 m, the discharge of the filler was stopped, and the spiral auger was pulled up to the ground while rotating backward.

The relationship between this depth and construction time is shown in FIG. The relationship between the replacement column and the depth is shown on the left side of FIG.
For comparison, as shown in FIG. 3 (b), while rotating the spiral auger forward, it digs up to a predetermined depth, rotates forward for 1 minute without discharging the filler, and then spiral auger. While discharging the filler from the tip of the container at a discharge rate of 100 liters per minute, the spiral auger is rotated at a speed of 0.35 m per minute while rotating forward, and when the GL-1 m position is reached, the discharge of the filler is stopped. This shows how to build a spiral auger that reverses and lifts it to the ground.

A vertical loading test was performed on each replacement column after the age of the filler in the replacement column constructed according to this example and the comparative example became two weeks or longer.
FIG. 4 shows the relationship between the amount of settlement at the tip of the replacement column and the load loaded on the head of the replacement column obtained from the results of these loading tests.

  As shown in FIG. 4, in the replacement column of the embodiment, as shown in (a), the initial subsidence amount is 0.9 mm at a replacement column head load of 300 kN, whereas the replacement column of the comparative example is (b). As shown, the displacement column head load is about 4.5 mm at 300 kN, and the present invention further reduces the initial settlement. The ultimate load is a load when the column tip sinking amount reaches 60 mm because the column tip sinking amount is defined as 10% of the column diameter. Therefore, the ultimate loads were 2850 kN for (a) and 2800 kN for (b), and no significant difference was observed between them.

  In addition, the amount of initial ground subsidence in the comparative example is large as shown in FIG. 5 (b) due to the auger digging, and the crack 4 is generated in the original ground G deeper than the predetermined ground, and the tip portion ground is According to the present invention, as shown in FIG. 5 (a), the filler can be filled into the crack 4, so that the looseness of the tip ground is eliminated and the filler is strengthened. It is estimated that the result was as follows.

In addition, the construction of the example and the comparative example is performed under the same conditions as above, and after 5 days from the construction, the surrounding column is excavated and the replacement column is lifted, the tip shape is observed and the tip is cut and the sectional shape is taken. Was observed.
In both the substitution column of the example and the substitution column of the comparative example, almost no earth and sand were mixed in at the lower end of the substitution column, and the substitution column exhibited the desired strength.

It is front explanatory drawing which shows embodiment of this invention to construction process order (a) (b) (c) (d) (e) (f) (g). It is explanatory drawing which shows a construction ground. It is explanatory drawing which shows the example of a construction process with a time-axis and a depth axis. It is a graph which shows the relationship between a loading load and a sinking amount. It is sectional explanatory drawing which shows the state beyond a predetermined depth.

Explanation of symbols

1 Screw auger 2 Replacement column 3 Cavity 4 Crack L1 Scheduled replacement bottom position L2 Scheduled replacement top position G Original ground

Claims (2)

  After the screw auger with the excavation part at the tip is rotated forward, the excavation is carried out, reaching at least 10 cm above the planned replacement bottom position of the column, and at most about the diameter of the replacement column to be built, Exclude the filler with a table flow value of 150-400 mm, which is not included, and when it is kneaded or constructed, by excavating from the tip of the screw auger with a forward rotation, and at the replacement bottom position of the column A column in which the soil is replaced with a filler by pulling up the screw auger while rotating it forward or reverse while discharging the filler from the tip end of the screw auger. Replacement building method.   While discharging the filler from the tip of the screw auger, the auger is pulled up by forward or reverse rotation, and when the upper end position of the column replacement is reached, the discharge of the filler is stopped, and then the auger is rotated forward or reverse. 2. A column replacement construction method according to claim 1, wherein the column is pulled up while being rotated.

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